Improved plunger and driver mechanism for analyzers

Abstract: In clinical analyzers, it is known to move a stack of test elements into position for dispensing by a plunger. However, known mechanisms for dispensing these test elements tend to comprise a complicated series of linking arms which convert rotary motion into linear motion. Described herein is an improved plunger and driver mechanism in which a plunger (23, 110, 112, 114, 116) is mounted in a housing (120). A spring (130) biases the plunger (23, 110, 112, 114, 116) to project beyond the housing (120). A first sensor (104, 142) senses the initial movement of the housing (120) and plunger (23, 110, 112, 114, 116) toward the stack, and a second sensor (132, 134, 136) senses movement of the plunger (23, 110, 112, 114, 116) against the action of the spring (130) back into the housing (120) upon contact with the stack.

Description: The present invention relates to an improved plunger and driver mechanism for advancing a stack of test elements located in an analyzer to a dispensing location for receiving patient samples. In clinical analyzers for assaying patient sample liquids, it is conventional to provide a stack of test elements from a depositor, each element of which is used to receive a portion of a patient sample liquid to do the assay. Such a stack features a plunger and a driver for the plunger, which press against one end of the stack to move its opposite end to a location to dispense of the test element into the analyzer. Means are also associated with the plunger, such as a bar code, for counting how far the plunger has moved, and hence how many test elements have been dispensed. An example of such an arrangement is known from the slide cartridges and plungers therefor used in "Ektachem"® analyzers, for example, the "E250" analyzer. In such a case, a driver for the plunger comprises a complicated series of linking arms which pivot to convert rotary motion from a DC motor into what is almost linear motion of the plunger. A spring appropriately connected at one of the pivot points ensures an almost constant biasing force on the plunger. Although such a mechanism has worked satisfactorily, it is less than ideal for several reasons. One is that its very complexity and large number of moving parts produces a low reliability. Another is all those parts lead to extra manufacturing costs. Still further, tolerance errors in all those parts can add up and thus lead to a departure from the desired "constant force" delivered by the plunger, or its desired linear movement. Finally, the linkage of the drive mechanism can produce vibrations which, because counting is via a bar code, produces a false count. It is therefore an object of the present invention is to provide a simplified, truly linear drive to a plunger which contacts and pushes a stack of test elements, to more positively control the force exerted against the stack as well as the "count" that the mechanism measures of the remaining elements in the stack. In accordance with the present invention, a plunger and drive mechanism for an analyzer which overcomes the above-noted problems is provided. More specifically, in accordance with one aspect of the present invention, there is provided an analyzer for detecting analytes in a patient liquid deposited on to a test element, the analyzer comprising:- a source of test elements arranged in a stack; a plunger mechanism for moving the stack linearly to a test element dispensing location, the plunger mechanism including a plunger element; drive means connected to the plunger mechanism for driving the plunger mechanism towards and away from the stack, the drive means including means for converting rotary motion into linear motion; and a patient liquid depositor for depositing liquid into a dispensed test element; characterized in that the plunger mechanism further includes a housing within which the plunger element is reciprocatingly mounted for linear movement, a portion of the drive means being mounted on the housing; biasing means for biasing the plunger element with respect to the housing, the plunger element being capable of moving into the housing against the action of the biasing means; and sensing means for sensing when the plunger element has moved into the housing against the action of the biasing means to generate a signal indicating that the plunger element has encountered the stack of test elements. Accordingly, it is an advantageous feature of the invention that a plunger and drive mechanism are provided in an analyzer, which ensure the plunger moves in a linear fashion, with constant force on the stack, while providing an accurate count of the test elements remaining in the stack. It is a related advantageous feature that such a plunger and drive mechanism are provided using a minimum of parts and expense. For a better understanding of the present invention, reference will now be made, by way of example only, to the accompanying drawings in which:- Figure 1 is a fragmentary sectioned elevational view illustrating one embodiment of test element stack arrangements in an analyzer; Figure 2 is a partially schematic, elevational view showing the prior art operation of the plungers of Figure 1; Figure 3A is a fragmentary sectioned elevational view of one embodiment of an improved plunger and driver mechanism constructed in accordance with the present invention as it is used with the embodiment of the analyzer shown in Figure 1 when carrying out dried assays; Figure 3B is a fragmentary sectioned view similar to that shown in Figure 3A, but of another sensor arrangement for the plunger and driver mechanism of the present invention; Figure 4 is a partly sectioned fragmentary elevational view showing a second embodiment of a plunger and driver mechanism as is it used in an analyzer for carrying out wet assays; Figure 5 is a fragmentary sectioned view taken generally along the line V-V of Figure 4; Figures 6 and 7 are elevational views similar to those shown in Figure 4, but of the plunger and sensors positioned in other than their "home" positions; and Figure 8 is a sectioned elevational view of one embodiment of the top portion of a stack of test elements used in the embodiment shown in Figures 4 to 7. The description which follows features the preferred embodiments, in which the plunger is demonstrated in its use for both so-called "dried" slide test elements of the type available from Eastman Kodak Company under the trademark "Ektachem" slides, and reagent cups used in wet assays with liquid reagents. In either case, patient sample liquid is deposited into them since, in the case of the slide elements, it is absorbed into or received by them in one form or another. In those contexts, preferred additional analyzer features are also described. In addition, the invention is useful regardless of the form of the test elements involved or the related analyzer apparatus, so long as the test elements are stored as, and the plunger operates on, a stack of them. Orientations such as "up", "above", "underneath" and the like refer to orientations of parts in their intended use. In one embodiment of the invention, an analyzer 10, Figure 1, utilizes dried slide test elements E and E' (of two different types), preferably held in place as a stack by means of a cartridge C which surrounds them. Although other mounting arrangements are possible for the cartridges, the cartridges can be provided, for example, in concentric tracks 22 and 24, separated by a wall 28. In this arrangement, they are removably supported on the top of movable rings 32, each for upward movement by plungers 23 into a slide dispensing position against a respective platen 21 which is biased by a spring 18 downwardly in a housing 201. Each platen is slotted at 30 to allow a slide element to be pushed through from a cartridge in the other track by a pusher blade 41, in the direction of arrow 19. The movement of the slide element proceeds, via the pusher blade, to a station 43 on support 51 where a depositor 55 deposits some patient sample liquid, in the direction of arrow 56, prior to the slide element being inserted into an incubator 50. When a cartridge C is depleted, it is dumped from its ring 32 by a mechanism 60, 80, 84, 86 and 90. The details of the dumping mechanism, and indeed of all the features shown in Figure 1, are conventional and are described in greater detail in US-A-5 089 418. An anti-backup plate 92 is conventional with such cartridges at the bottom of each stack. This platen moves up with the bottom-most slide element E or E', and stays at its last position until plunger 23 pushes it up further. This ensures that the remaining slides do not fall to the bottom when the plunger for that cartridge is temporarily pulled downward to allow another cartridge from either that same track (not shown), or the adjacent track, to be used to supply a slide element. The retention of the slides at the top of the cartridge means that the distance the plunger 23 has to move upward from a home position (the down-most position) until it contacts the anti-backup plate 92 and hence the stack, is a measure of the number of test elements used, and hence the number remaining, as will become apparent. Figure 2 illustrates the prior art method described above for driving plungers 23 linearly. A motor 93 turns a shaft on which is mounted a series of levers 94, 95, 96, 97 which convert the rotary motion of motor 93 into approximate linear motion. Lever 97 is pivotally fixed at 98 and attached to the plunger, and a spring 99 is judiciously connected to lever 97 to exert a more or less constant upward force on plunger 23. To sense the distance travelled by the plunger and hence the number of slide elements already used (and the number remaining), a bar code 100 is formed on the side of the plunger for scanning by reader 102. This construction has the drawbacks mentioned above, not the least of which is that there are at least six moving parts connecting the plunger to motor 93. In accordance with the invention, a greatly simplified driver is provided in Figure 3A. Plunger 23 comprises a projecting head 110, a shank portion 112, stop shoulders 114, and a flag portion 116. Shank portion 112 and stop shoulders 114 are confined within a housing 120 which is apertured at 122, 124 at its two opposite ends. Head 110 of plunger 23 projects through aperture 122, and flag portion 116 projects into, and out of when depressed, aperture 124. To bias plunger 23 upward so that flag portion 116 normally does not project out aperture 124, a compression spring 130 is mounted between plunger 23 and the housing. Annular bearing 131 is used to keep plunger 112 centered. Outside of aperture 124 is a sensing portion 132 of housing 120 on which is mounted a suitable sensor, such as an infrared diode and detector 134, 136 which emits and detects a beam of light traversing aperture 124. A shoulder 140 on portion 132 acts as a flag to trigger a similar second sensor 142 fixed to the analyzer. Both sensors 136 and 142 are connected to a computer 143 to calculate the number of slide elements remaining in a stack. To drive housing 120, a pinion gear 144 is driven by a suitable stepper motor (not shown). A rack gear 146 is mounted on the side of housing 120 to engage gear 144. Alternatively, a worm gear arrangement is also useful. In operation, head portion 110 of plunger 23 is biased upwardly, as shown by the solid line position, until plunger 23 contacts the bottom of the stack of elements E (actually, the anti-backup platen, not shown) remaining at the top of a cartridge (not shown). This occurs because gears 144 and 146 act to drive housing 120 and biased plunger 23 into contact. As soon as housing 120 starts upward, flag portion 140 uncovers sensor 142 and computer 143 registers a "zero" or home position, so that all half-steps, or whole steps if desired, advanced by the stepper motor for gear 144 can be counted. At the moment of contact between head portion 110 and the stack of elements, gear 144 continues to drive to force the cartridge and its stack into contact with platen 21, Figure 1, with spring 18 fully compressed. At this point, plunger 23 becomes stationary, so that flag portion 116, Fig. 3A, breaks the beam between diode 134 and detector 136. A signal is sent to computer 143, which stops driving gear 144 and registers that the stack of slide elements E has been contacted. The number of half- or whole steps the stepper motor has advanced is then calculated by the computer as the number of slide elements used up, and by subtraction, the amount remaining. Thus, it is no longer necessary to use a bar code label on the plunger. As long as head portion 110 is prevented from advancing upwardly by a cartridge, spring 130 in its compressed state delivers a constant expansion force against plunger 23 and the stack of slide elements, regardless of the number of slide elements present. An alternative to the use of second sensor 142 and shoulder 140 is to convert sensor 142 into a fixed flag 190, Fig. 3B, which projects into the path of the beam between 134 and 136 when the plunger and housing are in the home position, shown in Fig. 3B. Still further, it is not necessary that the plunger be restricted for use with a stack of dried slide elements. Nor, for that matter, need it be used only to push the stack upwardly. Figures 4-8 illustrate its use in a wet assay analyzer, so-called because the reagents are used in liquid, rather than dried, form. Furthermore, the stack of test elements is pushed downwardly, rather than upwardly, for ejection of a test element at the bottom, rather than the top, of a stack. Because the assay is a wet assay, the test elements now comprise a reagent cup "W", Figure 4. Any wet assay analyzer can be used with this invention, and there are many such available in the prior art. Conventionally, such an analyzer dispenses a reagent cup W from a dispensing location 221, into an incubator 250 comprising, for example, a rotor 252 with holding apertures 254, which rotates the cup W into position under a patient liquid depositor 256, to at least one reagent liquid depositor (not shown), and then to a read station (also not shown). (Stations downstream of the dispensing location 221 are not part of the invention and are not described further.) It is conventional when supplying such cups W to stack them, one inside the other, as shown, in a holder 260 apertured at 262. Inside aperture 262 at location 221 a lip 264 is provided to act as a retainer to retain the stack against falling out. Lip 264 can be either a complete annular ring in aperture 262, or only fragments thereof. A plunger 223 is also conventionally employed at the opposite end of the stack to apply driving pressure downward on the stack. In accordance with the invention, the driving of plunger 223 is achieved in the following fashion: Plunger 223 is mounted at one end of a rod 266 which loosely fits within a housing 268, which is preferably a lead screw. Housing 268 in turn is driven by a stepper motor in a linear actuator 270 fixed to the analyzer. Bottom end 272 of housing 268 is spaced away from plunger 223, preferably by a compression spring 274. Opposite end 276 of housing 268 terminates in a collar 278 having a split yoke 280, 282, Figure 5, between which is mounted a first sensor comprising, for example, an infrared diode 284 and detector 286. Additionally, yoke 280, 282 acts as a flag for a second sensor comprising a similar diode 288 and detector 290 fixed to the analyzer on portion 292. The end 294 of rod 266, Figure 4, which is opposite to plunger 223, extends out beyond and above collar 278 on housing 268. An L-shaped flag finger 296 is affixed to end 294, portion 298 thereof normally projecting into the beam of light emitted between diode 284 and detector 286, Figure 5. Because housing 268 also advances into aperture 262, its outside diameter D 2 , Figure 4, is preferably less than outside diameter D 1 of plunger 223. A computer 300 keeps track of and controls the operation of the plunger and its drive mechanism. In operation, the home position of collar 278 is that shown in Figure 4, that is, in its fully "up" position so that yoke 280, 282 interrupts the beam of light between diode 288 and detector 290. At this point, holder 260 can be moved into or out of position relative to plunger 223, so that a variety of such holders 260 can be sequentially positioned, particularly if each one is supplied with a reagent pre-attached to the inside wall of the cup. (Such a reagent can be, for example, an antibody specific to a particular analyte.) As linear actuator 270 causes housing 268 to advance downwardly, Figure 6, yoke 280, 282 uncovers detector 290 and a signal is registered on computer 300 that plunger movement has started. The number of steps used by the stepper motor of linear actuator 270, and hence the linear advance of housing 268 into aperture 262 is then counted. At this point in time, plunger 223 (not shown) on rod 266 has not yet encountered the stack of cups W, so that portion 298 of flag 296 still interrupts the beam of light generated at "A" by collar 278. Once plunger 223 does contact the top of the stack, Figure 7, rod 266 ceases advancing even though housing 268 continues. Hence, spring 274 starts to compress, and most importantly, portion 298 of flag 296 uncovers, in the direction of arrow 299, detector 290, sending a signal to computer 300 to stop advancing housing 268 and that the stack has been contacted. Calibration steps are used initially to determine and sense, using the plunger, that a) holder 260 is present and b) how far down within aperture 262 the top of a complete, unemptied stack is located. Thereafter, by calculating the distance Y, Figure 7, as a difference in terms of movement of housing 268 between sensor events, computer 300 easily determines the number of cups W already used, and by subtraction, the number remaining. To eject a cup W, either the spring 274 is used to generate a sufficient force when compressed from height h 1 , Figure 4, to height h 2 , Figure 7, to eject a cup past seal lip 264, Fig. 4, or an additional advance is given to housing 268 to bottom out on plunger 223 so as to force out a cup, in the direction of arrow 302. As an alternative to spring 274, a leaf spring 310, shown in phantom, Figure 4, can be used to bias plunger 223 downwardly beyond its housing. In that case, cup ejection is achieved by bottoming out housing 268 on to plunger 223. As yet another alternative, a septum 320 can be located above each uppermost cup W' in a stack, Figure 8, to preserve and protect any reagent pre-attached to that uppermost cup. The septum simply rests on the top edge of cup W'. If used, the septum remains in place between cup W' and the plunger, much as an anti-backup platen does in the cartridge in the embodiment of Figure 1. If septum 320 is not used, then cup W' can be used as a "septum", in which case preferably it is not supplied with a reagent pre-attached and is not used to conduct an assay. As yet another variation, it will be readily apparent that the positions of the sensor diode-detector, and flag, can be reversed, so that, for example, finger 296 becomes a sensing yoke on plunger 266, and collar 278 provides a flag that fits within such a yoke, Figure 5. Similarly, portion 292 on the analyzer can be a finger that breaks a beam of light generated between sensors on yoke 280, 282.

Claims: An analyzer (10) for detecting analytes in a patient liquid deposited on to a test element (E, E'; W; W'), the analyzer comprising:- a source (C; 260) of test elements (E, E'; W, W') arranged in a stack; a plunger mechanism (23, 110, 112, 114, 116, 120, 122, 124; 223, 226, 266, 268, 272, 276, 294, 296, 298) for moving the stack linearly to a test element dispensing location, the plunger mechanism including a plunger element (23; 223); drive means (144, 146; 268, 270) connected to the plunger mechanism for driving the plunger mechanism towards and away from the stack, the drive means including means for converting rotary motion into linear motion; and a patient liquid depositor (55; 256) for depositing liquid into a dispensed test element; characterized in that the plunger mechanism further includes a housing (120; 268) within which the plunger element is reciprocatingly mounted for linear movement, a portion (146; 268) of the drive means being mounted on the housing; biasing means (130; 274) for biasing the plunger element with respect to the housing, the plunger element being capable of moving into the housing against the action of the biasing means; and sensing means (134, 136; 284, 286) for sensing when the plunger element has moved into the housing against the action of the biasing means to generate a signal indicating that the plunger element has encountered the stack of test elements. An analyzer according to claim 1, wherein the sensing means comprises a sensor fixed to the housing and a flag (116; 298) fixed to the plunger element, the biasing means being effective to push the plunger element and the flag into or out of a position where it can be detected by the sensor. An analyzer according to claim 2, further including a second sensor comprising a flag (140; 280, 282) fixed to the analyzer (10) at a position effective to be detected by the sensor when the housing is in a "home" position. An analyzer according to any one of claims 1 to 3, wherein the portion of the drive means mounted on the housing comprises a rack gear (146), the drive means further including a pinion gear (144) meshed with the rack gear for linearly moving the rack gear, the housing and the plunger element. An analyzer according to any one of claims 1 to 4, wherein the test elements are slide test elements (E, E'), the analyzer further including a slide element dispenser (41) for dispensing a slide element from the stack at the dispensing location. An analyzer according to claim 5, wherein the movement of the plunger element against the biasing means is effective to generate a uniform force to uniformly bias each of the slide elements (E, E') in the stack into the dispensing location regardless of the number of the slide elements present in the stack. An analyzer according to any one of claims 1 to 3, wherein the movement of the plunger element against the biasing means is effective to generate a uniform force to uniformly bias each of the test elements in the stack into the dispensing location. An analyzer according to any one of claims 1 to 3, wherein the housing comprises an externally threaded lead screw. An analyzer according to claim 1, further including counting means for counting the number of test elements remaining in the stack. An analyzer according to claim 9, wherein the counting means comprises second sensing means including a second sensor (142; 290) fixed to the analyzer (10) in a position to detect the plunger element or the housing when the plunger element or the housing is furthest away from the stack, a second flag (140; 298) on the plunger element or the housing, and a computer (300) to calculate the number of test elements which can fit within the distance represented by the second sensing means being triggered by movement of the second flag away from the second sensor, and the first sensing means being triggered when the plunger element contacts the stack so as to determine the number of test elements already dispensed.

Inventors: JAKUBOWICZ RAYMOND FRANCIS, MARVIN RUSSEL H, PORTE JOHANNES JACOBUS, JAKUBOWICZ, RAYMOND FRANCIS, MARVIN, RUSSEL H., PORTE, JOHANNES JACOBUS
Applicants: JOHNSON & JOHNSON CLIN DIAG, JOHNSON & JOHNSON CLINICAL DIAGNOSTICS, INC.
Application year: 1994
Main classification: G01N35
IPC codes: G01N35